The present invention relates to a displacement type fluid machine, such as a pump, a compressor or an expander.
The gyration type displacement type fluid machine of this kind (referred to hereinafter simply as a "gyration type fluid machine") has been proposed in Unexamined Japanese Patent Publication No. 55-23353 (Publication 1), U.S. Pat. No. 2,112,890 (Publication 2), Unexamined Japanese Patent Publication No. 5-202869 (Publication 3) and Unexamined Japanese Patent Publication No. 6-280758 (Publication 4).
The gyration type fluid machine, as disclosed in any of Publications 1 to 4, has essentially advantageous features as a displacement type fluid machine in that it has multiple cylinders and a completely balanced rotating shaft, so that it produces lower in pressure pulsations and vibrations and a lower relative sliding rate between a displacer and a cylinder, thereby to reduce the frictional loss.
However, the stroke of the individual working chambers, to be formed by a plurality of vanes including a displacer and a cylinder, from the completion of the suction to the completion of the discharge is as short (e.g., about one half of the rotary type and equal to that of the reciprocating type) as about 180 degrees in terms of a shaft rotation angle .theta., so that the flow velocity in the discharge process is so high as to increase the over compression loss, thereby to cause a problem of reduction in performance. In the fluid machine of this type, on the other hand, a rotating moment to rotate the displacer itself acts as a reaction from the compressed working fluid upon the displacer so that the moment is applied to the contact point between the cylinder and the displacer. In the structure disclosed in any of Publications 1 to 4, however, the working chambers from the completion of the suction, to the completion of the discharge are concentrated on one side of the drive shaft. As a result, the rotating moment acting on the displacer grows excessive thereby to invite a defect in that the performance and reliability are degraded by the wear on the vanes. Unexamined Japanese Patent Publication No. 9-268987 (Publication 5) has proposed a displacement type fluid machine as a gyration type fluid machine to solve that defect.
Now, in order to achieve a high efficiency in a displacement type fluid machine in which one space is formed by the inner wall face of a cylinder and the outer wall face of a displacer when the center of the displacer is located at the center of rotation of a rotating shaft, and in which a plurality of spaces are formed when a positional relationship between the displacer and the cylinder is located at the position of gyration, it is necessary to lower the fluid friction loss and the mechanical friction loss and to minimize the internal leakage of the working fluid which will occur through the gap (i.e., the radial gap) of the sliding portion between the displacer and the cylinder forming the working spaces (or working chambers).
In the a conventional machine in which the cylinder and the displacer are so contoured that a gap of a predetermined width (or a gyration radius) is formed between the cylinder and the displacer when they are made concentric, however, the radial gap is enlarged by the clearance of the shaft drive system for moving the displacer and by the rotating moment acting upon the displacer to increase the internal leakage of the working fluid thereby to cause a problem that the machine performance is lowered.
When the eccentricity of the drive shaft is increased to enlarge the gyrating radius of the displacer so as to reduce that radial gap, on the other hand, the displacer contacts the outer peripheral portion of its contour with the cylinder so that a seriously excessive load (or the reaction of the contact portion) acts upon the drive shaft because of the small contact angle leading to a problem of reduction in reliability, such as seizure of the shaft.